Radio direction finding system



c. c. CNES gli fifi-5 RADIO DIRECTION FINDING SYSTEM Filed Jan. ll, 1934 5 Sheets-Sheet 2 Loop cfg/QL C @JQ/VES @y amg Feb., 14? ww C. JQNES m4263425 RADIO DIRECTION FINDING SYSTEM Filed Jan. 1l, 1934 3 Sheets-Sheet 5 HHHHH HHHHH LOOP l F/6f4 ma f//Mmm 5 @QW @m ATTORNEKS Patented Feb. 14, 1939 UN-l'iED STATES T`lAfllglT @FFI-1 RADIO DIRECTION FINDING SYSTEM CarlC. Jones, Clayton, Ohio Application January 11, 1934, Serial No. 706,236

3 Claims. (01.-'250-11) (Granted under the act of March 3, k1883, as amended April 30, 1928; 370 O. G. 757) The invention described herein may be manutively; also a polar diagram representing the facturedand used by or-for the Government for field pattern resulting from the combination governmental purposes, vwithout the-payment to thereOf. me f any royalty thereon, The invention contemplates a directional re- This invention relates to a radio direction nndcelver of Wave energy such as a loop operatively ing system, and more speciiically to a directional "Connected to a device which alternately switches radio receiving system which will provide means the phase 0f Slleh energy; modulates said refor indicating aurally and/ or visually a true sense CeiVed energy With a frequency differing from vof direction of a source of radio'waves, that is the freqlleney Of the reCeVed Wave energy, and

lo to say, the direction vfrom a point of reception then COmbneS this modulated energy with the l0 to a source of transmission of electro-magnetic energy frOln a non-directional antenna, vthe weve energy without ambiguity and uncertainty, source of the latter being lthe same radio waves An object 0f the invention is to give accurate which-energize the loop receiver. The resultant bilateral indication and to define one trueA course Waves of energy thus combined are then sub- .;,3 Without-,ninety degree 0r one hundred vand eighty 'jectedvto the action of a detector or rectifier, the vn;

degreenembiguity, output of which is introduced into the circuit of Another object is to provide a device capable a balanced rectier'in a manner described hereofbeing `added as a unit to standard radio reinafter InOre in detail. RadiO frequency empliceiver equipment with a minimum of adjustment eatiOnmay be `introdlleefi immediately prier 60 ,20 and a minimum of mechanical parts, rectification or detection, and audio frequency A further object of the invention is to proamplifica-tion may be introduced after detection 'vide means which will operate both on modu- Or rectification, if desired.

lated and unmodulated radio waves, and which `The balanced rectier is acted upon by the s-will not destroy the vcharacteristics of the re- -reetifled eembinetiOn 0f the 100D and l10n-direccelved signal. Other objects and advantages will -tional antenna energy in such a manner that the appear as the description proceeds. ldeviation of the loop from a plane normal to The structural organization-and mode of op- "the direction of travel of the incoming Wave-will eration of a preferred embodiment of the invencause the needle of the zero-center indicator, tion will now be described with reference to the inthe' balanced rectifying circuit, to deiiect either accompanying drawings, in which: right or left from its center-zero position and 30 Fig. 1-diagrammaticallyillustrates.a system in the direction of deection so indicated is the di- -which the principles of the invention are aprect function ofthe direction of rotation of Vche plied in conjunction with a radio receiving -aploop `from the plane normal to the direction of paratus of Va type well known in the art; ftravel of the radio wave. The visual indicator Fig. 1c showsan alternative form of balanced may, at the will or Adesire of the designer, Show 35 rectifier circuit arrangement; a deflection to the right of the zero-center for a Figs. 1b and 1c show bridge circuitsrepresentright-hand rotation of the loopffrom the normal ing conditions to be satisfied by any balanced plane, and a left deflection for a left rotation rectierfarrangement such as here shown by way of the loop from the normal plane; or the reverse 40 of example; action may be obtained. In either case the re- 40 `Figs. 1d and le show further balanced circuit ciprocal bearing will give opposite deflection, arrangements in accordance with the principles that is, if one reciprocal gives right and left deof the invention; iiection for right and left rotation respectively, Fig. 2 depicts a practical and convenient emthe opposite reciprocal Will give left and right ibodiment for applying `the principles disclosed deflection for right and left rotation, respective- 45 Agenerally in Fig. 1; 1y. Since there are but two zero indications for Figs. 3a to 3h graphically depict changes in 360 degrees rotation of the loop, there are no the `wave forms at different progressive stages ambiguities for "the reasons just set forth.

of the operation; It will thus be seen that the device embody- Fig. .4 illustrates oppositely disposed angular 'ing this invention enables radio position or di- Y50 positions 'of the loop or directional receiver of rection nding under either fixed lor mobile conwave energy; and ditions; ifurthermore, it enables a mobile craft Fig. 5 shows polar diagrams graphically repor vehicle to lproceedin a direct line toward or resenting the energy received by the directional away from an `emitter of radio energy, unless the -loop 'and the vnon-directional antenna, respecprocedure lin Asuch a direct line is prevented by 55 other agencies or conditions without the scope of this device.

Furthermore, the device comprising this invention is capable of attachment to and use with any standard radio receiving system and does not destroy the intelligibility or Volume of the signal on which a bearing or direction is being observed.

Referring to Fig. 1 or Fig. 2, the loop consisting of a multiplicity of turns of wire is resonated by oondensers Ci and C2, the center point between such condensers being grounded, although the ground is not essential to operation. The terminals of the loop are connected to plates PLI and PL2 of a thermionic vacuum tube or tubes through condensers C3 and C4 which are of a value to present an effective impedance to the alternating voltage applied to the plates of the vacuum tube or tubes. The plates of the vacuum tube or tubes are energized by alternating voltage from secondary SI of transformer TI through inductances LI and L2, which offer an effective impedance to the ow of radio frequency energy from the loop to the secondary winding Si.

The center point ofsecondary winding SI is connected through a resistor Ri to the cathode of the vacuum tube or tubes. A ground may be applied at point f in this circuit and is here shown although its use is not necessary to proper operation. The terminal of resistance RI which leads to the cathode or cathodes is connected to the input terminal of a radio receiver. To the same input terminal is connected the non-directional antenna A through resistor R2 whose Value of resistance is not critical and which may or may not be required depending upon the effective height of the non-directional antenna. The remaining input terminal of the radio receiver is grounded. The output terminals of the radio receiver are connected to primary P2 of transformer T2 in the balanced rectifier circuit.

The primaries of transformer, T3 in the balanced rectifier circuit R and the primary of transformer TE in the electrical switching cir-V cuit generally designated at S are energized from a common alternating current source D which may be an alternator, a vacuum tube generator, or any other form of alternating current generator. Y

The balanced rectifier circuit R comprises a single full-wave rectifier tube; but a pair of two element tubes may be employed or any tube or tubes with a multiplicity of elements, or any rectifier so connected as to perform essentially the same function. The plates of the vacuum tube or tubes are energized by secondary S3 of transformer T3 in a manner essentiallyV at 180 degrees phase difference.

The common cathode K is connected through secondary S2 of transformer T2 to slider B on resistor R3 which shunts indicator I, which is inserted at the mid-point of secondary winding S3. Condenser C5 is not essential to operation, but its use when properly selected, increases the efficiency thereof.

Balanced rectifier circuit R is not limited to the specific circuit arrangement shown in Fig. 1,

but may be of the form shown in Fig. 1a, or of,

any other form of circuit arrangement that will satisfy the conditions of Fig. lb or lc.

Referring now to Fig. 4 and assuming the loop to be physically rotated an angle a from the position of minimum reception, so that a radio frequency potential exists at the loop terminals. With the loop in this position, consider the action in circuit S Fig. l. When an Aalternating current, preferably of sine wave form, is introduced in the primary PI and transferred electromagnetically to secondary SI of transformer TI, it will be seen that when plate PLI is positive with respect to the cathode, plate PL2 is negative with respect to the cathode, and vice versa. W'henV plate PLI is positive, the current will flow between the cathode and plate PLI and a modulated radio frequency voltage of phase will appear across resistor R2. At this instant plate PL2 is negative and there is no current flow between the cathode and plate PL2. When plate PL2 becomes positive, there is a current flow between the cathode and plate PL2 and a modulated radio frequency voltage of phase wir) occurs across resistor RI. Thus, the phases of the radio frequency voltage within its modulated envelope occurring across resistor RI are shifted electrically essentially 180 in phase when plates PLI and PL2 alternate in becoming positive in potential. The modulated radio frequency energy occurring across resistor RI is combined with the radio frequency energy from the nondirectional antenna A and introduced in the input circuit of the radio receiver. The phase of the radio frequency energy in the non-directional antenna A is essentially qb or wir). Thus it will be seen that the vertical antenna energy is additive to the radio frequency in one phase and subtractive to the radio frequency which is essentially 180 out of phase. The envelope of the radio frequency energy as presented to the detector or rectifier in the receiver is of the general form shown in Fig. 3.

The output from the rectifier or detector after being amplified, if desired, will appear in primary winding P2 of the transformer T2 in the general form of c shown in Fig. 3, and will be essentially the fundamental frequency fo which was introduced into primary PI.

In a like manner, it can be shown that if the loop is physically rotated from the point of minimum reception of the loop in the amount of any angle (Fig. 4) which is opposite in sign to the angle a just considered, that the resultant output voltage from the detector or rectifier, which will appear in winding P2, will be of the form e", Fig, 3, and will be plus or minus 180 out of phase with voltage e.

Thus, it will be seen that in winding P2 there will appear voltage e or c", dependent upon whether the loop is turned one direction or the other from its minimum receptive position. These voltages, e and e, are transferred to secondary S2 and flow through the indicator I in a manner and with the result that Will be described hereinafter.

Referring now to the balanced rectifier circuit R of Fig. l. The primary winding P3 of transformer T3 is energized from the same alternating current source D as is primary winding PI of the transformer TI. Thus, plate PL3 will become positive at the instant that plate PL4 becomes negative in potential, and vice versa. The action of circuit R can best be understood by referring to Fig. 1b, which is a schematicarrangement of circuit R in which a single fullwave rectifier tube is employed, although the action is similar when copper oxide or other forms of rectiers are used. When plate PL3 becomes positive, the current fiow will be from PLS to point C, thence through S2 to B. At this point the current Will divide in inverse proportion to the resistances of the parallel paths, and one portion ofthe `current Will pass through vpart of R3 from point B to pointA, then through ysecondary winding S3 to PL3. One portion of the current dividing at point B (ii) will pass through R3 to point D, then through indicator -I to point A, ywhere it will flow through a section of S3 to PLS. It will be noted in this instance that no current flows from point D to point C via plate PLli since the latter is at a negative potential and effectively opposes the ow of current.

When plate PL becomes positive, plate PLS becomes negative. The current flow is then from plate PL to point C, thence through S2 to point B where the current divides in a manner previously explained. One portion of the current ows through a section of R3 to point D, thence through secondary winding S3 to PLQ. The remaining portion of the current flows from point B through R3 to A, thence through indicator I to point D (i2), thence through S3 to PL4. It will be noted that the current does not divide at point A since the plate PLS is negative, as has been previously explained.

It will also be noted that currents il and i2, Fig. 3(1), ow in opposite directions through indicator I. Therefore, during one complete cycle of fo (from source D) there will occur two opposing currents through indicator I and, thus, voltage e", Fig. 3U), is produced across indicator I. With a properly damped indicator I and a frequency fo` properly chosen, indicator I will not indicate each opposing pulse but will-give a steady deflection proportional to the algebraic difference ofv currents il 'and i2. Slider B on resistor R3 is set so that with no energy introduced in S2 from P2 the condition zI-z'2=0 obtains, and the indicator will show a steady reading at the center zero position.

The alternating voltage e or e, Fig. 3(6), which has been explained, as existing in primary circuit P2, is transferred electromagnetically to secondary S2, and flows through indicator I, in a manner about to be described, where it is combined with e", and there results an algebraic sum of these two alternating current voltages.

Assuming now that voltage e (equal to or less than e) is induced in secondary S2 in phase with e in S3, and now consider that portion of the cycle when F (Fig. lb) is positive in potential and G is negative at the time when PL3 is positive and PLd is negative. The current flow will be from F to point B where the current divides in inverse proportion to the resistance. One portion ilows through R3 to A, thence to C via PLS and back to G. The remaining portion flows through R3 to point D, thence through indicator I to A, (i3) through S3 to PLS thence to C and G. Thus i3 is additive to and in phase with il. In this half cycle there is no current ow from D to C via PLQ, since PL is negative. Also, i2 does not ow in this half cycle.

Consider now the second half of the cycle. G and PL4 are now positive and F and PL3 are negative. The current flow (due to e) is from G to C, thence to K2. Thus the potential of K2 tends to become positive and PL tends to become negative by reason of e which is in opposition to e and, therefore, all or part of i2 is cancelled, dependent upon the voltage relations. Thus, if e and e" are equal, i2 is balanced out and the resultant current through indicator I for complete cycle of e' plus e' is of the form shown in Fig. 3(y) which will result in a steady deflection of indicator I from its zero position.

In a like manner, it can be shown that a combination of e and e" will result in diminishing z' I and increasing i2, (Fig. 3(1)), which will result in a deflection of indicator I opposite to that obtained above for e Vplus e"'. The vaction can be vsimilarly explained for other voltages relations between e', e and e".

lIt will be noted that in the circuit shown in Figures la, 1b and lc that the current through the indicator I is Vin opposing direction for each succeeding half cycle. That is, the indicator meter will .receive two opposing pulses Vper cycle which are of a period diiering from the natural period of the meter and are, therefore, not indicated. Figures 1d and le illustrate a method-by which the alternating current from the secondary S3, when rectified, will pass throughthe indicating meter in such a manner that, in absence of any signal from the receiver, the current through the meter is balanced at all times. Referring .again in Figure 1d, it will -be seen that if plate PLI and plate PLQ are positive at the instant that plates PL2 and PL3 are negative, current through the indicating instrument I is balanced at all times providing point X on resistor R3 is properly chosen. Also, when plates PL2 and PLS are positive, which occurs at the;

time when plates PL! and PLi are negative, the rectied current through the indicator is likewise balanced. Thus, in absence of a signal'from the receiver (e or 6") no current flows through the indicating meter and the pointer remains in the center 'zero position.

A further advantage of this circuit may be realized by assuming a signal (e or e") induced in secondary S2a and S217. As previously explained, these voltages (e' or e) appear in th output of the receiver when the loop antenna is turned either one direction or the other from its minimum receptive position. Applying the analysis employed in the explanation of Figure 1b,

it can be shown that in Figure 1d that a directional pulse due to e will appear through indicator I in both halves of the cycle of voltage e,

instead of one directional impulse per cycle of e" as would be the case in the use o-f the circuit of Figure 1b. Thus, the circuit of Figure 1d when ,l

considered over a multiple of complete cycles of 6"', will result in a current essentially twice as great as that obtained with circuit Ib, therefore, rendering the device more sensitive to small signal inputs. Figure le is essentially the same as Figure 1d except that it shows the arrangement when copper oxide or other forms of rectiers are employed.

It will thus be seen that the device of this invention can be so constructed or arranged that a turning of the loop to the right of its minimum receptive position will show a right deection on the indicator I, and that a rotation of the loop to the left oi its minimum receptive position will cause a deflection to the left of zero on indicator I.

Thus, it will be seen that the device of this invention may be employed for such purposes as position or direction finding; to track a mobile body; to guide a mobile body toward or away from an emitter of radio energy, or for any other purrents received in said directive antenna system, means for securing from currents induced in said system resultant currents having a frequency equal to the frequency ofrsaid local source, an amplitude dependent uponV the deviation of a line perpendicular to the plane of said antenna system from a line joining the center of said system and the'source of incoming radiations, and a phase dependent upon the sense of said deviation, a course indicating device, an output switching circuit for alternately supplying said resultant currents to the terminals of said course indicating device, and separate means separately and inductively coup-led to said local source for separately energizing said modulating circuit and said output switching circuit.Y

2. A direction indicating system comprising a directive antenna system for receiving incoming radio frequency radiations, a local source of alternating current, a circuit for modulating cur-V rents received in said directive antenna system, means for securing from currents induced in said systemV resultant currents having a frequency equal to the frequency of said local s-ource, an

amplitude dependent upon the deviation of a line perpendicular to the plane of said antenna system from a line joining the center of said system and the source of incoming radiations, and a phase dependent upon the sense of said deviation, a course indicating device, an output switching circuit for alternately supplying said resultant currents to the terminals of said course indicating device, and separate Vmeans separately and inductively coupled to said local source for separately energizing said modulating circuit and said output switching circuit, said means including separate transformers, each of said transformers being provided with secondaries having separate windings.

3. A direction indicating system comprising a directive Vantenna system for receiving incoming radio frequency radiations, a local source of alternating current, a circuit for modulating currents received in said directive antenna system, means for securing from currents induced in said system resultant currents having a frequency equal to the frequency of said local source, an amplitude dependent upon the deviation of a line perpendicular Vto the plane of said antenna system from a line joining the center of said system and the source of incoming radiations, and a phase dependent upon th-eisense of said deviation, a course indicating device, an output switching circuit for alternately supplying said resultant currents to the terminals of said course indicating device, .and separate means separately and inductively coupled to said local source for separately energizingV said modulating circuit and ysaid output switching circuit, said means comprising a transformer having separate primary and separate secondary windings operative with said modulating circuit and a transformer having separate secondary windings operative with said output'svvitching circuit.

CARL C. JONES. 

